refactor: split types.ts into domain modules (phase 4, step 1)

Split 1,443-line types.ts into 14 focused domain files under src/types/:
common.ts, session.ts, task.ts, app-state.ts, respawn.ts, ralph.ts,
api.ts, lifecycle.ts, run-summary.ts, tools.ts, teams.ts, push.ts,
plan.ts, and index.ts barrel.

Moved PlanItem interface from plan-orchestrator.ts into types/plan.ts
to break circular dependency. Original types.ts replaced with barrel
re-export — zero changes to 36 import sites.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/plan-orchestrator.ts

@@ -20,36 +20,10 @@ import type { TerminalMultiplexer } from './mux-interface.js';
 import { existsSync, mkdirSync, writeFileSync } from 'node:fs';
 import { join } from 'node:path';
 import { RESEARCH_AGENT_PROMPT, PLANNER_PROMPT } from './prompts/index.js';
-import { PlanTaskStatus, TddPhase } from './types.js';
+import type { PlanItem } from './types.js';
 
-// ============================================================================
-// Types
-// ============================================================================
-
-/** Development phase in TDD cycle (alias for TddPhase) */
-export type PlanPhase = TddPhase;
-
-/**
- * Plan item with TDD structure.
- */
-export interface PlanItem {
-  id?: string;
-  content: string;
-  priority: 'P0' | 'P1' | 'P2' | null;
-  source?: string;
-  rationale?: string;
-  verificationCriteria?: string;
-  testCommand?: string;
-  dependencies?: string[];
-  status?: PlanTaskStatus;
-  attempts?: number;
-  lastError?: string;
-  completedAt?: number;
-  complexity?: 'low' | 'medium' | 'high';
-  tddPhase?: PlanPhase;
-  pairedWith?: string;
-  reviewChecklist?: string[];
-}
+// Re-export for backward compatibility
+export type { PlanItem };
 
 export interface ResearchResult {
   success: boolean;